Gas anchor



Mmm B29 E957 w. P. mmm-mm2 mm MW GAS ANCHOR Fild Aug. V6 1953Smets-Sheet l TTRNE'Y zwYAmmw mm; @EMM mmm.. z... @FMEA /m @im B, F MmmmJ n N L p55@ j VN Mmmm HZ E957 Lm. P. mEncHERTZ afa-AL mw GAS ANCHORFiled Aug. 17, 1953 2 Sheets-Sheet 2 Fi?, yE

i PAUL F E.U:.1F11LE.'1=TZ El I f EARL H .1' EANJJEEHG DA1-,1L AnEDNNALLY JH.,

y TEHEN/:E A; FDLLAHD Y i JNVENToRs ATTDHNEY GAS ANCHOR Paul P.Reichertz, Dallas, Carl R. Sandberg, Grand Prairie, and Carl A.Connally, Jr., and Terence A. Pollard, Dallas, Tex., assignors, by mesneassignments, to Socony Mobil Oil Company, Inc., a corporation of NewYork Application August 17, 1953, Serial No. 374,762

'7 Claims. (Cl. 10S-203) This invention relates to the` separation ofgas from gas-liquid mixtures on a continuous basis and relates morespecifically to a bottom hole gas anchor employed in oil weils.

in earth formations where petroleum oil is found, the petroleum oil isfrequently intimately associated with gas, which causes considerablediliculty in those instances where the oil has to be pumped from thewell. The gas occupies a part of the displacement volume of the pump,reducing the volumetric eciency of the pump, and, if present insufdcient quantities, will cause a complete cessation of the delivery ofoil by the pump.

The entrained gas may exist in the form of free gas in bubbles ofvarious sizes. These bubbles of free gas have a rate of rise in agas-liquid mixture which is a function of the size of the bubbles. Thelarger the bubbles, the more rapidly they rise in a gas-liquid mixture.The gas anchors which are in general use depend upon this characteristicof the gas bubbles for their success in opera tion. The conventionaltype gas anchor consists of a chamber in which fluids must tlow downwardfor some distance in order to enter an opening to a pump intake port.The gas which separates in the chamber of the anchor escapes throughports provided near the top of the chamber. In this type anchor theseparation of the gas is dependent upon the bubbles of gas rising at arate faster than the downward rate of flow of the gas-liquid mixture inthe anchor chamber. Small bubbles of gas whose rate of rise is equal toor less than the downward rate of the gas-liquid mixture will not beseparated by this type anchor. As considerable quantities of gas areencountered in the form of small bubbles having a low rate of rise,there is a definite need for a gas anchor which will separate thesesmall bubbles.

ln addition to preventing gas entering the oil pump, `it is alsodesirable to prevent solid particles entering the pump and causingdamage to it.

lt is an object of this invention to provide a gas an-` chor which willseparate from gas-liquid mixtures gas in the form of small bubbles whichcannot be separated by the usual type of gas anchor. this invention toprovide a means of increasing the volumetric efcency of subsurface oil`well pumps in those instances wherein gas entering the pump is asignificant factor contributing to decreased efficiency of pumping. ltis a further object of this invention to prevent entry into the pump ofsolid particles which would damage the working parts of the pump. Theseand further objects of this invention will be understood from thefollowing description of the invention taken in connection with theaccompanying drawings in which:

Fig. l is a view in section of a gas anchor constructed in accordancewith one embodiment of `the invention. Fig. 2 is an enlarged view insection of the lower end of the porous tube of a modified version oft-he gas anchor shown in Fig. 1. Fig. 3 is a view partially in sectionand partially in elevation of a gas anchor constructed in accordancewith another embodiment of the invention.

It is another object of i ICC In the drawings 1 represents the wall ofan oil well or the casing of an oil well adjacent to an oil-producingformation. A cylindrical anchor shell 2 is closed at its lower end byinternally threaded collar 3 and externally threaded bull plug 4. Collar3 is pressed into the lower end of anchor shell 2 and welded in place asshown. Bull plug 4 is threadedly engaged within collar 3. Near its upperend, anchor shell 2 contains a plurality of ports 5 for entry of agas-liquid mixture and a plurality of ports 6 for escape from anchorshell 2 of separated gas. Welded to the upper end of anchor shell 2 isinternally threaded collar 7. Bushing or coupling 3, which is internallyand externally threaded and forms a central iiow channel for liquids, isthreadedly engaged to collar 7. t will be recognized here that, ifdesired, bushing 8 could be secured directly to the upper portion ofanchor shell 2, thus dispensing with collar 7. Secured to the lowerportion of bushing 8 is an eduction tube which comprises swag 9, pipe10, collar 11, swag l2, collar 13, porous tubes 14 and 15 and bull pluglo, and forms an exclusive path for flow of liquids into bushing 8. Swag9, which contains external threads on its lower end, is pressed into thelower portion of bushing tl and welded in place. Pipe 10, externallythreaded at both ends, is secured to the lower end of swag 9 byinternally threaded collar 11, and swag 12, which is externally threadedat its upper end, is secured to the lower end of pipe liti by internallythreaded collar i3. Porous tube lid is securedto the lower end of swagl2, and porous tube l5 is secured to the lower end oftube 14j Attachedto the lower end of tube 15 is bull plug 16.

ln the embodiment of the invention shown in Fig. 2

the gas anchor of Fig. l has been modified by provid ing a pressurerelease valve in the bull plug lo at the lower end of porous tube 15.Referring to Fig. 2, the pressure release valveli! is secured withinbull plug lo which, in this form of the invention, has a port ldpositioned in its lower end. Pressure release valve i7 is designed toopen when a predetermined pressure drop across the walls of the porous`tubes is exceeded. When pressure release valve 17 is open, well fluidsow upward into the inside of the porous tubes and out of the anchorthrough pipe lil. Thus, it can be seen that, in this embodiment, theporous tubes will function unless the flow of iuids through them isimpeded by the plugging of their pores or by `the collection of solidmatter on the outer surface of the tubes, and in that event the anchorwill function as does a conventional anchor. This feature is ofadvantage in those instances where it is not desirable to cease pumpingin the event the porous tubes cease to function. The anchor may beremoved for cleaning whenever it is convenient to do so and need not beremoved if the eciency of the porous tubes is materially reduced or theybecome inoperative.

ln the embodiment of the invention shown in Fig. 3, shell i9 s securedtothe lower end of collar 7 by Welding.` Shell 19, which functions toprotect the porous tubes from damage while the gas anchor is beinginstalled or removed from awell, is constructed in the form of a hollowcylinder having a large number of 'openings or perforations 20 therein.Theseopenings or per forations Ztl are sufficient in number and size topresent negligible impedance to the iiow of well fluids to the po roustubes. In another embodiment `of the invention, not shown, protectionmay be provided the porous tubes by using, in lieu of shell i9, a wireframework positioned in spaced relation about the porous tubes andsecured at its upper end to the lower end of collar 7. These lastmentioned forms of construction are used where it is desirable to allowlarge gas bubbles, which would normally separate as the well fluidsinitially enter the anchor, to

rise past the porous tubes to; aid in agglomerating orf` removing thesmall gas bubbles accumulating on the outer walls of the porous tubes.

It will be evident from the above that in those instances where threadsor welding are used to join various members other recognized means ofjoining metal parts may be used if desired. Thread connections arepreferable where used in the interest of easy assembly and disassemblyfor purposes of cleaning and replacing broken or Worn parts.

The porous material of the tubes operates much more efficiently as afilter if it is presaturated with the liquid it is to pass. In oilwells, water is usually produced to some extent, so porous tube 14 isprovided for the purpose of passing oil while porous tube 15 is providedfor the purpose of passing water. Before the anchor is put intooperation, each of these tubes is presaturated with the liquid it is topass. In order to lter from the gas liquid mixture the portion of gaswhich would be detrimental to the pumping operation yet not have anexcessive amount of gas released from solution, it is necessary that thepressure drop across the walls of the porous tubes be as small aspracticable, with the upper limit not being more than one pound persquare inch.

The proper dimensions of the tubes and the proper permeability of theporous material must be utilized to limit the pressure drop across thetube walls to less than one poundper square inch. For satisfactory gasseparation the permeability of the porous material should be limited toa range of from one to thirty darcies. Also, the dimensions andpermeability of tubes 14 and 15 must be so related to each other thatthe pressure drop across the walls of both tubes will be the same forthe oil-water ratio existing in the well in which the anchor is beingused. This is necessary to prevent any tendency on the part of theporous tubes tol cause either water or oil to accumulate within theanchor. The relationship of the factors involved in determining thepermeability and size of the porous tubes is expressed in an equationfor the flow of fluids through porous media known as Darcys equation, aform of which is oMLn@ where:

P=uid pressure drop across the walls of the porous tube inpounds persquare inch.

Q=quantity of uid flowing through the porous tube in barrels per day.

rizinner radius of porous tube in inches.

r0=outer radius of porous tube in inches.

M :viscosity of flowing fluid in centipoises.

L=length of porous tube in inches.

K=permeability of the porous material in darcies.

. The factor 10.66 is a conversion factor to make the equationconsistent for the units used.

P, as stated previously, must be limited to one pound per square inch orless. Q, the quantity of uid flowing through the porous tube, may bemaintained a constant. M, the viscosity of iiowing fluid, for the oilwill vary depending upon the oil being produced, while the M for thewater is nearlyk enough a constant that it may be taken as the same forall wells. L, the length of the porous tube, may be varied as needed,although it should not be so great that the tubes are too fragile andditlicult to handle. K, the permeability of the porous material, asstated above, `should be chosen in the range between one to thirtydarcies for satisfactory gas separation. The upper limit of the outerradius, ro, is determined by the size tube Which may be used in thewell. The thickness of the tube walls, ro-ri, may be varied as needed toachieve the desired pressure drop across the walls, keeping in mindthatv they must not be made so small as to Oil production- 50 barrelsper day Water productionbarrels per day Oil viscosity at bottom holeconditions-25 centipoises Water viscosity at bottom hole conditions--onecentipoise Assume use of porous material of following specifications:

For oil-30 darcy permeability, inner radius one inch,

outer radius 11A; inches.

For water-two darcy permeability, inner radius one inch,

outer radius 1% inches. Y

Limit the pressure drop across the walls of the porous tube to 0.1 poundper square inch.

Based upon these well conditions and assumptions, the length of the tubefor oil flow is:

= 83.6 Vinches and the length of the tube for Water is:

L=10-66Xm l 0l inches The porous material of which tubes 14 and 15 aremade may be sintered metal, Alundum, Aloxite, or other porous materialswhich have the desired permeability, can withstand well conditions, andmay be worked into the desired form and size. If sintered metal is used,it may be manufactured from powdered metals such as brass or stainlesssteel, which are not subject to corrosion due to contact with thevarious gases and fluids encountered in oil wells.

Prior to using the gas anchor, the porous tubes 14 and 15 are saturatedwith oil and Water, respectively. The anchor is then assembled, attachedbelow a deep Well oil pump to a producing string by means of bushing oand lowered to the producing zone in an oil well. Upon the starting ofthe pump the gas-liquid mixture ows into the anchor through ports 5 andthen flows downward within shell 2. The larger bubbles of gas willseparate and pass out through ports 6 as the mixture flows downward inthe anchor. The mixture containing the small bubbles of gas flows towardthe porous tubes. The oil ows through tube 14 and the water through tube15, the small gas bubbles being separated from the oil and water by thefiltering action of the tubes. The small bubbles collect on the outersurface of the tubes, agglomerato into larger bubbles of gas, and passup the anchor and out through ports 6 in shell Z.

lIf the pores of the porous tubes become clogged with solid particles inthe well fluids or the surfaces of the tubes become covered with solids,the pump may be raised from its seat to allow the fluids in the pumpingstring to ow back through the anchor and `flush out the tubes.

Although the porous material used in this embodiment `of the inventionis in the form of tubes, it will be apparent that it may be used innumerous other forms.

Having thus described our invention, it will be understood that such`ydescription has been given by way of illustration and example `and notby way of limitation, reference for the latter purpose being had `to theappended claims;

We claim:

1. In a gas anchor the combination of an eduction tube, at least aportion of which is composed of porous material having a permeability ofbetween one and thirty darcies, and means for securing said eductiontub-e to a producing string.

2. In a gas anchor the combination of a liquid eduction tube, at least aportion of which is composed of a porous material having a permeabilitybetween one and thirty darcies, a pressure release valve positioned inthe lower end of said eduction tube, and means for securing saideduction tube to a producing string.

3. In a gas anchor the combination of a tubular member closed at itslower end and containing a plurality of ports near its upper end, meansfor connecting said tubular member to a producing string, a liquideduction tube closed at its lower end positioned in spaced relationwithin said tubular member and secured at the upper end thereof to saidlast-mentioned means, at least a portion -of `said eduction tube beingcomposed of a porous material having a permeability between one andthirty darcies.

4. In a gas anchor the combination of a tubular member rclosed at itslower end and containing a plurality of ports near its upper end, meansfor connecting said tubular member to a producing string, a liquideduction tube positioned in spaced relation within said tubular memberand secured at the upper end thereof to said lastmentioned means, atleast a portion of said eduction tube being composed 'of a porousmaterial having a permeability between one and thirty darcies, and apressure release valve positioned in the lower end of said eductiontube.

5. Means for transmission of liquids and the separation of gases in theproduction from a well comprising a coupling having a central lowchannel, a rigid, hollow cylindrical structure supported by saidcoupling `and having perforations such as to present negligibleimpedance to flow of said liquids and said gases, and a structurependantly supported from said coupling within said cylindrical structureforming an exclusive path for flow of liquids in said well to saidcentral flow channel comprising a cylinder of porous material, saidmaterial having a permeability between one and thirty darcies.

6. Means for transmission of liquids and the separation of gases in theproduction from a well comprising a coupling having a central ilowchannel, a rigid, hollow cylindrical structure supported 'by saidIcoupling and having perforations such as to present negligibleimpedance to flow of said liquids and said gases, and a structurependantly supported from said coupling within said cylindrical structureforming an exclusive path for ow et liquids in said well to said centralflow channel cornprising a cylinder of porous material, ysaid materialhaving a permeability of between one and thirty darcies, and a pressurerelease valve secured in the lower end of said cylinder.

7. in a gas anchor the combination of a tubular member having aplurality of ports therein over substantially its entire length, meansfor connecting said tubular member to a producing string, a liquideduction tube closed at its lower end positioned in spaced relationwithin said tubular member and `secured at the upper end thereof to saidlast mentioned means, at least a portion of said eduction tube being`composed of a porous material having a permeability between one andthirty darcies, and pressure release valve positioned in the lower endof said eduction tube.

References Cited in the le of this patent UNITED STATES PATENTS1,329,171 Garry Jan. 27, 1920 1,749,216 Goldman Mar. 4, 1930 2,104,339Arutunoff Jan. 4, 1938 2,111,758 Davis Mar. 22, 1938 2,234,977 OhlandMar. 18, 1941 2,291,378 Courtney July 28, 1942 2,346,602 OBannon Apr.11, 1944 2,439,468 Hopkins Apr. 13, 1948 2,506,790 Ihrig et al May 9,1950 2,523,091 Bruce Sept. 19, 1950 2,525,897 Greene Oct. 17, 19502,528,448 Munk Oct. 31, 1950 2,665,644 Wells Jan. 12, 1954

